The effects of pentobarbitone anaesthesia on the volume and composition of the extracellular fluid of dogs.

1. The effects of pentobarbitone sodium (Nembutal) anaesthesia in dogs on extracellular fluid and plasma volumes, plasma protein concentration, haematocrit and extracellular fluid electrolyte composition were measured.2. Induction of pentobarbitone anaesthesia caused a rapid rise in extracellular fluid volume, accompanied by decreases in the haematocrit, in extracellular fluid potassium concentration, and in plasma calcium, magnesium, and protein concentrations. There were no significant changes in plasma osmolality and extracellular fluid concentrations of sodium and chloride.3. Extracellular fluid volume did not alter significantly during six hours of anaesthesia, but the haematocrit and extracellular fluid potassium concentration showed an increase towards control values.4. The relevance of these findings to the interpretation of experiments carried out under pentobarbitone anaesthesia is noted.